Imagine Sheldon as Kramer, Leonard as Jerry and Howard and Raj as George and one of his many enablers.
The structure is basically identical, except Kramer at least had some kind of legitimate contrivance that necessitated Jerry to go out of his way for him. This show doesn't even bother with that. We're just made to believe that we should give a crap about Sheldon's concerns because he's Sheldon.
And, Rather than dig into the comedy of Sheldon dealing with life without Leonard , we're left to imagine his dealings with the general public, whereas in Seinfeld, we might get to see Kramer run into a ne'erdowell out on the mean streets resulting in some great physical comedy moments.
What's most perplexing is we don't really get a resolution to the episode. BBT tells us that Sheldon never changes, Leonard tells Sheldon that nothing needs to change really, except that they don't need an agreement to be friends, which is basically a pointless conclusion to the story. So we're left with a hollow jab at a meaningful "hug" at the end of the episode that doesn't actually have any real impact.
Of course, Seinfeld did this for years, but it never pretended to be meaningful. It never wanted you to come away from an episode learning anything. This is exactly what reviewers mean when they rate things based on "what they're trying to achieve." If you want to have an affecting show that illustrates nuanced and realistic changes in its characters, then make that show. If you're not capable of doing that, make Seinfeld. Larry David never tried to make a show with character development. That's why he gets a pass. But this isn't doing that, and that's why it doesn't.